Abstract:

To explore the resource utilization of phosphogypsum in road base materials， this study conducted basic mechanical tests， freeze-thaw and dry-wet cycle tests， dry shrinkage tests， expansion tests and pollutant leaching tests. A comparative study was performed on the road performance of two base layers： phosphogypsum composite stabilized crushed stone base （phosphogypsum powder replacing fine aggregate） and phosphogypsum artificial aggregate base （phosphogypsum artificial aggregate replacing coarse aggregate）. The results show that both materials meet the mechanical requirements for road application. Due to the low cylinder compressive strength， high crushing value and high soft stone content of artificial aggregate， the 360 d unconfined compressive strength of phosphogypsum artificial aggregate base is 6.12 MPa lower than that of the phosphogypsum composite stabilized crushed stone base. The two materials have comparable frost resistance and water stability， but present significant differences in dry shrinkage behavior. The phosphogypsum composite stabilized crushed stone base exhibits slight expansion with a 60 d dry shrinkage coefficient of -0.13×10^-6 με/%， while the phosphogypsum artificial aggregate base suffers severe dry shrinkage with a coefficient of 195.42×10^-6 με/% and more obvious performance degradation under dry-wet alternating conditions.In terms of volume stability， the phosphogypsum artificial aggregate base barely expands with a cumulative expansion rate of only 0.03%， while the phosphogypsum composite stabilized crushed stone base reaches 0.35% owing to ettringite formation. The property differences are mainly attributed to the various content of ettringite， C-S-H gel and structural compactness. Furthermore， the leaching concentrations of total phosphorus and fluoride of the two materials fully comply with the current class Ⅲ standard for surface water.

Key words: phosphogypsum, artificial aggregate, road base, road performance, pollutant leaching test